The present invention is directed to a device for cutting a patella during knee surgery, such as total knee arthoplastic surgery. Due mainly to osteoarthritis (degenerative joint disease), though as well to other causes such as rheumatoid arthritis and trauma, the patella may need surgery, where the cartilage and some of the bone thereof are cut off and replaced by a prosthesis colloquially termed a "button". The prosthesis replaces the diseased cartilage and bone, and provides a new flat surface by which the patella with the prosthesis may be returned to its normal position against the femur.
The patella, commonly called kneecap, is that part of the human skeleton that is approximately 1.5-2 cm. in thickness having an articular surface of cartilage. The articular surface is held in place against the distal portion of the femur (the femoral condyles) by the patella tendon. The patella provides the leverage necessary for proper functioning of the knee joint. If the articular surface of the patella becomes damaged, or if the bone of the patella decays or is degenerative, proper functioning of the knee joint is not possible, with the concomitant pain and immobility associated therewith. If it be found that it is possible to replace a portion of the patella along with the articular surface in order to restore the knee joint to its normal functioning by providing the proper tensioning of the tendon holding the patella in place, surgery will be performed on the patella, during which the knee area is exposed and the patella everted such that the articular surface of cartilage is flipped over so that it faces away from the femoral condyles. After this has been achieved, the surgeon, as is the current practice, will direct an assistant to firmly hold the everted patella in place what are termed "towel clips", which actually resemble a pair of tongs that, in scissor-like fashion, can be operated to sandwich at its pointed tips the patella, at portions below the plane in which the surgeon is to cut the patella. The plane in which the surgeon will cut is preferably parallel to the flat articular surface of the patella and a desired distance therebelow, the distance being enough such that the prosthesis, or button, when implanted, will allow the patella to be approximately the same thickness as a normal, healthy patella, with due regard being directed to the age and size of the person whose patella is being fitted with the button and any special circumstances associated therewith.
The current practice among orthopedic surgeons is to choose the plane of cut of the patella by eye, and then, using a conventional oscillating saw, to cut through that plane to provide an approximately flat surface at a certain depth below the original articular surface that the surgeon feels will adequately accept the prosthesis and allow for proper functioning of the knee joint. After the surgeon has cut the patella through the plane and removed the diseased portions of the patella along with other bone, he next inserts the prosthesis by drilling a hole into the remainder of the patella bone. The prosthesis itself has a stem portion of 4 mm. depth, and integral therewith is the button having a depth of 9 mm. for a large person, and 81/2 mm. for a small person. After the hole has been drilled, the stem is forced into the hole, thereby firmly implanting the prosthesis to the flat, cut and exposed surface of the patella. Thereafter, the surgeon will rotate the patella with implant 180 degrees to reposition it into its normal functioning location and orientation, with the surface of the botton now taking the place of the original articular surface of the patella.
It is common, however, that the surgeon, upon the repositioning of the patella with implant, will find that he has not removed enough of the patella to provide proper functioning of the knee joint and proper tensioning of the tendon holding the patella. Thus, the surgeon will evert the patella a second time, remove the implanted button with stem, and cut through the patella a second time in another plane, to thereby remove more of the patella. Then, he will again implant the prosthesis, and rotate the patella with implant a second time, to see if it now fits properly. This procedure is repeated as many times as it is necessary until the proper amount of patella has been removed to allow for implantation of the prosthesis and until the proper positioning and functioning of the patella with implant has been achieved.
Two requirements are essential to the above operation: good bone-to-prosthesis control, and enough patella left after cutting so that the stem of the prosthesis will have sufficient and proper anchorage. Since according to the way the cutting of the patella is presently carried out, which is by the surgeon's approximating where the plane of cut should be and then cutting therethrough by holding the oscillating saw in his hand, precise horizontal and flat surfaces are often not achieved, simply because of the guessing involved in determining the plane of cut, which must be horizontal and must be flat for proper fitting of the prosthesis and the proper functioning thereof.
Thus, the surgeon must be very careful and make a first cut in a plane that usually turns out not to have been deep enough. Further, when the surgeon repeats such steps, he again is very careful, only cutting off slightly below that plane in which he previously cut, thus ofttimes necessitating third, fourth or even more cuts, and the ensuing repositioning and eversions of the patella associated with each cut. Also, because the oscillating saw is hand-held, it is not uncommon for the surgeon to have cut the patella in a way that has not provided a flat surface necessary for the proper positioning of the prosthesis.
All of these above-noted disadvantages and drawbacks to the presently-used procedure for cutting the patella have caused excessive guessowrk to be employed in an operation requiring great skill, where cutting is required within extremely close tolerances, and have caused time-consuming operations because of the need to repeat the steps many times over, until the right cut is made. Further, it is also possible that, under presently-used techniques, too much bone may be cut off, if the surgeon is not extremely careful, thus dooming the knee operation to at least partial failure. In addition, the surgeon presently is in need of at least one assistant, who, utilizing the towel clips, firmly attaches them to the patella and holds the patella thereby. However, two assistants are often used for this purpose.